Orserdu (elacestrant) is a prescription oral tablet used to treat certain types of breast cancer in some adults. Orserdu can cause side effects that range from mild to serious. Examples include nausea and muscle pain.

Some people may experience mild to serious side effects during Orserdu treatment. Examples of the drug’s commonly reported side effects include:

Mild side effects have been reported with Orserdu. These include:

  • decreased appetite
  • cough and shortness of breath
  • nausea and vomiting
  • abdominal pain
  • headache
  • fatigue
  • upset stomach or heartburn
  • muscle and joint pain
  • hot flashes
  • diarrhea or constipation
  • dizziness
  • rash
  • insomnia
  • low level of hemoglobin in the blood
  • mild allergic reaction*†

In most cases, these side effects should be temporary. And some may be easily managed. But if you have symptoms that are ongoing or bothersome, talk with your doctor or pharmacist. And do not stop taking Orserdu unless your doctor recommends it.

Orserdu may cause mild side effects other than those listed above. See the drug’s prescribing information for details.

* To learn more about this side effect, see the “Side effects explained” section below.
† An allergic reaction is possible after taking Orserdu, but this side effect wasn’t reported in studies.

Serious side effects have been reported with Orserdu. These include:

If you develop serious side effects while taking Orserdu, call your doctor right away. If the side effects seem life threatening or you think you have a medical emergency, immediately call 911 or your local emergency number.

* To learn more about this side effect, see the “Side effects explained” section below.
† An allergic reaction is possible after taking Orserdu, but this side effect wasn’t reported in studies.

Note: After the Food and Drug Administration (FDA) approves a drug, it tracks and reviews side effects of the medication. If you’d like to notify the FDA about a side effect you’ve had with Orserdu, visit MedWatch.

Get answers to some frequently asked questions about Orserdu’s side effects.

How do side effects of Orserdu compare with those of Faslodex?

Both Orserdu and fulvestrant (Faslodex) are prescribed to treat certain types of breast cancer. These drugs have some similar side effects and others that vary.

Side effects that both Orserdu and Faslodex can cause include:

  • nausea and vomiting
  • headache
  • decreased appetite
  • increased liver enzymes

To learn more about how Orserdu and Faslodex compare, talk with your doctor or pharmacist. You can also see this article to learn more about the side effects of Faslodex.

Does Orserdu cause long-term side effects?

It’s possible. Orserdu can cause high cholesterol and triglyceride levels. If left untreated over time, high levels of cholesterol or triglycerides can increase your risk of heart attack or stroke. Your doctor will regularly check these levels before, during, and after your Orserdu treatment.

Talk with your doctor to learn more about possible side effects of Orserdu and how long they may last.

Learn more about some of the side effects Orserdu may cause.

Increased liver enzymes

In studies of Orserdu, increased liver enzymes was a common side effect. This can be a sign of liver damage. Symptoms of liver damage include:

  • decreased appetite
  • abdominal pain on the upper-right side
  • jaundice (yellowing of the skin or the whites of your eyes)
  • dark yellow or brown urine
  • fatigue
  • nausea or vomiting
  • weight loss

Factors that can raise your risk of having increased liver enzymes with Orserdu include:

* An infection is active if it’s currently causing symptoms.

What might help

If you have increased liver enzyme levels during Orserdu treatment, in some cases, your doctor may decrease your dose or have you temporarily stop taking the drug. They’ll likely order frequent lab tests until your liver enzymes return to a safe range.

If you’re concerned about increased liver enzymes with Orserdu, talk with your doctor or pharmacist.

High level of creatinine in the blood

In studies of Orserdu, a high level of creatinine in the blood was a common side effect. This can cause symptoms such as:

  • dark yellow or brown urine
  • decreased urine production
  • weakness
  • fatigue
  • nausea or vomiting

Factors that can increase the risk of a high creatinine level with Orserdu include:

What might help

Your doctor may recommend increasing your fluid intake if you have a high creatinine level during Orserdu treatment. In some cases, your doctor may have you temporarily stop taking Orserdu until your level returns to a safe range.

If you’re concerned about a high creatinine level from Orserdu, talk with your doctor or pharmacist.

Allergic reaction

Like most drugs, Orserdu can cause an allergic reaction in some people. But this side effect wasn’t reported in studies.

Symptoms of an allergic reaction can be mild to serious and can include:

  • rash
  • itchiness
  • flushing (temporary warmth, redness, or deepening of skin color)
  • swelling under your skin (usually in your eyelids, lips, hands, or feet)
  • swelling of your mouth, tongue, or throat, which can make it hard to breathe

What might help

If you have mild symptoms of an allergic reaction, such as a mild rash, call your doctor right away. They may suggest a treatment to manage your symptoms. Examples include:

  • an oral antihistamine, such as diphenhydramine (Benadryl)
  • a product you apply to your skin, such as hydrocortisone cream

If your doctor confirms you’ve had a mild allergic reaction to Orserdu, they’ll decide whether you should continue taking it.

If you have symptoms of a severe allergic reaction, such as swelling or difficulty breathing, call 911 or your local emergency number right away. These symptoms could be life threatening and require immediate medical care.

If your doctor confirms you’ve had a serious allergic reaction to Orserdu, they may have you switch to a different treatment.

Keeping track of side effects

During your Orserdu treatment, consider taking notes on any side effects you’re having. You can then share this information with your doctor. This is especially helpful when you first start taking a new drug or using a combination of treatments.

Your side effect notes can include things such as:

  • what dose of the drug you were taking when you had the side effect
  • how soon you had the side effect after starting that dose
  • what your symptoms were
  • how your symptoms affected your daily activities
  • what other medications you were taking
  • any other information you feel is important

Keeping notes and sharing them with your doctor will help them learn more about how Orserdu affects you. They can then use this information to adjust your treatment plan if needed.

Below is important information you should consider before taking Orserdu.

Warnings

Orserdu can sometimes cause harmful effects in people who have certain conditions. This is known as a drug-condition interaction. Other factors may also affect whether Orserdu is a good treatment option for you.

Talk with your doctor about your health history before you take Orserdu. Be sure to tell them if any of the following factors apply to you:

Alcohol and Orserdu

There are no known interactions between alcohol and Orserdu. But Orserdu can increase your liver enzymes, and alcohol can also have this effect.

If you drink alcohol, talk with your doctor or pharmacist about how much (if any) may be safe to consume during Orserdu treatment.

Pregnancy and breastfeeding with Orserdu

Before starting Orserdu treatment, it’s important to tell your doctor if you’re pregnant, breastfeeding, or planning to become pregnant or to breastfeed.

Pregnancy

Orserdu is not safe to take during pregnancy because it can cause harm to a fetus.

If you’re able to become pregnant, your doctor will do a pregnancy test before prescribing Orserdu to make sure you’re not pregnant. They’ll also recommend using a form of birth control during Orserdu treatment and for 1 week after your last dose.

If you become pregnant while taking Orserdu, contact your doctor right away.

Males* who take Orserdu and have a partner who can become pregnant should use birth control during treatment and for 1 week after their last dose.

* In this article, we use the term “male” to refer to someone’s sex assigned at birth. For information about the difference between sex and gender, see this article.

Breastfeeding

Orserdu is not safe to take while breastfeeding. You should not breastfeed during Orserdu treatment or for 1 week after your last dose.

If you’re breastfeeding or planning to do so, talk with your doctor about your options.

Like most drugs, Orserdu can cause a number of side effects that range from mild to serious. However, most are temporary and go away after a few days to weeks. If you have questions about side effects that Orserdu can cause, talk with your doctor.

Examples of questions to help get you started include:

  • Are there specific foods that can make the side effects of Orserdu worse?
  • How severe are the hot flashes with Orserdu?
  • Which side effects of Orserdu need immediate attention?

To learn more about Orserdu, see this article.

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Disclaimer: Healthline has made every effort to make certain that all information is factually correct, comprehensive, and up to date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or another healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.